In vitro sensitivity of antimalarial drugs and correlation with clinico-parasitological response following treatment with a 3-day artesunate-mefloquine combination in patients with falciparum malaria along the Thai-Myanmar border

- The parasite clearance time (PCT) in patients with 'Late Parasitological Response' was significantly prolonged compared with 'Adequate Parasitological Response' and re-infection.
- Declining in vitro artesunate and mefloquine sensitivity has been observed in Plasmodium falciparum isolates collected from 'Late Parasitological Failure (LPF)' patients compared to 'Adequate Clinical and Parasitological Response (ACPR)', and re-infection.
- The correlation between in vitro sensitivity of Plasmodium falciparum isolates to artesunate and PCT suggests that the in vitro susceptibility information is a reliable tool to predict clinico-parasitological response following a 3-day artesunate-mefloquine.

A 3-day artesunate-mefloquine combination therapy has been using as first-line treatment for acute uncomplicated Plasmodium falciparum malaria in Thailand since 1995 on the background of mefloquine resistance. The aim of the present study was to assess sensitivity of P. falciparum isolates (n = 44) in an area along the Thai-Myanmar border (year 2009) to artesunate, mefloquine, chloroquine and quinine, including their correlation with clinico-parasitological response. Twenty, 19, and 5 isolates were collected from patients with 'Adequate Clinical and Parasitological Response (ACPR)', 'Late Parasitological Failure (LPF)' and 're-infection', respectively. The IC50 of artesunate and mefloquine were significantly higher in patients with LPF compared with ACPR and re-infection. The proportion of isolates with declined artesunate or mefloquine sensitivity in the LPF group (47.4%) was significantly higher than the ACPR group (5.0%). A weak but statistical significant correlation (r = 0.384, p = 0.01) was observed between IC50 values of artesunate and parasite clearance time (PCT). There was no significant relationship between in vitro sensitivity of parasite isolates to chloroquine or quinine and clinical response. In vitro susceptibility of P. falciparum isolates to artesunate and mefloquine may be used as a useful reliable tool to predict clinico-pathological response following a 3-day artesunate-mefloquine combination therapy.

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